The Siren
by ShiTiger
Summary: A siren finds himself trapped in Derry's river after a heavy rainfall. (slash Billy/Pennywise)
1. Fresh Blood

**Ch 1: Fresh Blood**

* * *

There was fresh _blood_ in the water. The siren's green eyes narrowed into slits as it swam down the canal toward the delicious scent. Even in his ravenous state, the creature was careful to stay underwater until the last possible moment.

A young man was splashing about in the shallower water as his crimson lifeblood continued to pour from his injuries. If Billy got any closer, he'd be exposed to whatever was above, but… _food._ He'd been trapped in this strange river since the heavy rains washed him over a high wall during the last moon cycle. There weren't enough fish, even in the deeper pool he'd discovered and claimed for his temporary home, to properly feed a siren, and the only humans he'd glimpsed were children.

Ever since the accident, Billy couldn't bring himself to hunt children. They were too great a reminder of his brother's unfortunate fate. But this human was not a child. Perhaps not an adult, but far too old to be considered a child. He could make a fine meal.

The siren felt his predator side rising to the surface, and his conscious mind fled in the face of such overwhelming hunger.

 _ **FOOD, EAT, HUNT,**_

 _ **DEVOUR!**_

The siren surged out of the water, razor-sharp teeth bared as he shimmied his body over the rocks. Without a thought for any danger that might be waiting for him, he wrapped his arms around the young man's twitching body and sunk his teeth into his neck to end his struggles.

In his hunger, Billy failed to notice the golden eyes peering at him from the mouth of a nearby sewer opening. He'd never glimpsed the zombie children that had, only moments before, chased the young man from the cavernous place, and into the water.

 _ **MEAT!**_

Billy ripped out the dark-haired boy's heart and bit into it, closing his eyes as he savored the salty taste of blood dripping down his throat. Still warm, still delicious. He hadn't feasted on a human in many, many cycles. This human would feed him for some time. And Billy knew the perfect place to stuff the body. Down in the darkness of the lake, beneath the falling water. The children never dove down that far.

"Hi-yah, friend! Enjoying your food?"

The siren's eyes popped open, his clawed hands digging into the lean body of his meal in shock. Narrowing his green eyes, the young creature hissed at the strange being that was standing far too close for comfort. It was oddly human-like, but also different. Pale skin, strange clothes, blood red hair, and a predator's grin.

"Haven't seen one of your kind in loooong time. However did you get stuck in my canal?" the towering man purred.

Billy dragged the dead body in his arms closer, his eyes darting around for a quick escape route, only to realize that he'd come too far into the shallows to feast. He should have dragged the human into the deeper water first. The siren cursed at himself, his fear rising as the odd being tilted its head at him in amusement.

"Don't worry, you can keep this boy. I know how to share," the man chuckled. Drawing itself up, the tall being announced, "I'm Pennywise, the Dancing Clown! And this is the entrance to my home."

The clown pointed to the round human-made opening behind him, before turning his attention back on the partial-fish boy that had managed to drag his catch a few inches back toward the water.

"Oh, I wouldn't try to run away, Billy," the clown insisted, stalking forward to tower over the siren.

"H-how do you k-know my n-name?" Billy asked, meeting the man's golden gaze. There was something oddly alluring about the not-human's eyes. Something that kept him rooted in the spot, unable to dredge even a single song from his throat – even if that song might guarantee his freedom from the strange hold the man had over him.

"I know a lot of things, Billy-boy. I'll make you a deal. I'll let you keep young Patrick here, and I'll even bring you more humans to feast on, in exchange for your… company," the man commented.

"My company?"

"It gets lonely being the only monster in Derry," the clown sighed, frowning dramatically. "You can stay in my town, and come to visit me here. I'll bring you flesh to keep you from starvation, and you can sing for me."

"Sing? Yes, I could do that," Billy murmured aloud.

"Good. Oooh, I should bring you a child next time. Their flesh is so much more flavorful," the older creature insisted.

"NO!"

"No?" the clown pouted at him, clearly taken aback.

"No. I don't eat children - not since Georgie…" Billy looked away, wishing desperately to be back underwater where it was safe and dark.

"Hmmm… that's too bad. I'll bring you older humans then, my vicious little siren. And you and I will be the best of _friends_."

* * *

Note: I planned for this to be a short ficlet, but it turned into a longer story.


	2. The Hot Mermaid

**Ch 2: The Hot Mermaid**

* * *

"Are you sure you saw a mermaid in the lake, new kid?" Eddie asked, glancing at the plastic bag Stanley was carrying that contained several, recently purchased, fresh market fish.

"Uh huh. I saw her swimming near the waterfall. She had long brown hair and pale skin," Ben stated.

"Was she hot?" Richie blurted out, forcing his way into the conversation.

"She was pretty far away. I think so, though," Ben answered. A moment later, he seemed to have another concerning thought. "Do you think she'll come out during the day? She's probably scared of people."

"She probably doesn't exist," Stanley grumbled, wondering how his friends had talked him into parting with his allowance to help them buy the fish he now had to carry.

"Brilliant, Holmes," Richie announced. "We'll meet back here an hour before dark, and then we'll go feed her."

"What about the curfew?" Eddie asked.

"Sneak out, stupid. Are you really gonna let your mom stop you from meeting a HOT mermaid?" Richie's arm wove around his shorter friend's shoulders, and he pulled him close with a grin.

"What if she's _not_ hot?" Stanley asked, in that 'you're such a hormonal idiot, Richie,' way of his.

"She's a MERMAID! That automatically makes her hot," the be-speckled boy insisted.

"What if she eats… people," the newest member of the Loser's Club asked, his voice barely above a whisper.

"Why would she eat people?" Richie sighed, shaking his head in amazement.

"I saw this anime once. It was called Petshop of Horrors, and the mermaid ate a guy… then turned into a giant fish," Ben insisted.

"That's a cartoon, Ben. Not real life," Stanley answered. It was obvious that, out of the four of them, he CLEARLY didn't believe in Ben's so-called mermaid.

* * *

Billy stayed near the bottom of the lake as another dead fish dropped into the water above him. Hesitantly, he grabbed at the nearest sinking fish, and bit into it. A grimace crossed his face as the cold, but stale flesh slid down his throat. Pennywise was clearly spoiling him if slightly old fish seemed unpleasant.

It reminded him of the long ago days when his parents would take him hunting. Once in a while, they would come across surface walkers who had drowned. And, if they were still in good enough shape, the family would feast on their bloated bodies. The inner meat was the most savory, even if it wasn't fresh. His parents had promised that they'd take him and Georgie on a proper hunt someday, when they were older. But that day never came, and now Billy was the last of his family.

The siren's musings were interrupted by a loud splash that echoed through the water. Tilting his head back, the creature could make out chubby human legs paddling pathetically in the water above.

A delicious thought swam through Billy's mind, and made him smile a toothy grin. Perhaps Pennywise was playing with him, and the chubby human in the water above was the MAIN COURSE! Churning his tail back and forth, the siren raced to the surface. In his delight, he completely overlooked the fact that it was still daytime until he surged out of the water in an impressive air jump.

"There SHE is!"

Green eyes darted to the young boys on the shore, then down to the heavy-set boy staring up at him in wonder. Moments later, he flopped back into the water – his landing ruined by the unexpected reality of his situation. Humans _saw_ him!

A flailing body caught his attention. It was the chubby boy from before. He must have been dragged under the water when Billy landed. In a daze, the siren watched as the chubby boy breathed in a mouthful of water. His struggle to get back to the surface intensified, but soon his pale-skinned body grew limp.

Billy felt his concern growing stronger with each moment. He hadn't meant to KILL the boy! Maybe he could still save him.

Dashing forward, he grabbed the boy's thick arms and pulled him to the surface. With his tail, he swam them both closer and closer to the water's edge, until he finally had the boy lying on his back on the rocky shore. Careful not to strand himself on land, Billy made sure to keep enough of his tail in the water to escape quickly if he needed to.

"Is Ben okay?" the cutest of the three boys on shore asked.

Billy's instincts curled fiercely inside of him, causing him to bare his teeth and hiss at the children. The boys drew back in fear, but their eyes continued to gaze with concern at their unconscious friend.

The siren bit back a growl and sighed in acceptance. He was really doing this. He was leaving himself exposed above water in an attempt to save a human's life. Breathing in deeply to fill his rarely-used lungs, the siren pressed his cold lips to the boy's, and attempted to push the air back into him.

After several attempts to breathe the boy back to life, and one firm slap to his chest (which was more out of frustration), the child's hefty body surged with life. In that moment, Billy caught a glimpse of a tall, familiar figure spying on them curiously from the woods.

"W-what's going on? Eeep!" The boy was staring up at him in amazement, Billy realized, once he'd torn his gaze away from the other creature.

"The mermaid totally _smooched_ you back to life!" the boy wearing the funny metal and glass contraption over his eyes yelled.

"Mer-maid?" Billy hissed in contempt, his tail splashing the water in annoyance.

"Sorry, um, merboy?" the taller child asked, looking sheepish.

"S-s-siren. And I am clearly _NOT_ female," Billy insisted, glaring at the annoyingly loud one for daring to refer to him as one of THOSE creatures.

"I've read about you. You… you sing sailors into the ocean, and watch them drown," the cute one said, whispering the last part as he leaned closer to the annoying one.

"Some of us do," Billy agreed, turning his green-eyed gaze back on the chubby human beneath him. "Why were you throwing stale fish into the water, human child?"

"Um… we wanted to feed you. T-there's not many fish in this river now that it's closed off by the dam," the boy stammered.

"Dam?"

"It's like a big wall that keeps the water from getting too high," the tall one answered.

Billy's eyes narrowed into slits as he hissed under his breath at the thought of those humans trapping him in their dying river. If it wasn't for Pennywise, he would have already starved to death.

"Um, we're sorry. We didn't make the dam, the adults did," the cute one explained.

"I do not blame you," the siren growled, pushing himself back into the water until he was chest deep in the soothing liquid. He stared at the children for a long moment, unsure of how to end their conversation. That was when he noticed the sun sinking in the distance.

A quick glance at the forest behind the children revealed that Pennywise had disappeared again, but Billy could feel his gaze. The other creature was lurking in the shadows somewhere nearby. And, despite the siren's insistence that he would not eat children, he knew that the clown did not adhere to any feeding guidelines except his own. These boys would be **fish to the slaughter** if they did not leave soon.

* * *

 _(The Losers Club POV on meeting their mermaid)_

The trio took several steps back in shock when the mermaid leapt out of the water and into the air above Ben's head. Her hair was long and brown, her eyes a brilliant green in the sunlight, and her breasts… okay, they were rather small. In fact, from where they were standing, it seemed like she had a slightly boyish chest. Maybe she was a teenage mermaid, and still developing her womanly qualities. That would make her closer to their age.

Those thoughts aside, the mermaid seemed as shocked to see them as they were to see her. Rather than flow gracefully back into the water, she landed awkwardly on her shoulder, sending the water high into the air.

When the wave cleared, both her and Ben were gone.

"She's got Ben!" Eddie cried out, puffing on his inhaler in panic.

"Richie, what do we do?" Stanley exclaimed, gesturing frantically at the river.

"I'm thinking!" Richie answered loudly.

His thinking clearly took too long, because suddenly Ben's upper body broke the surface, followed by the mermaid. She was holding his unconscious form as she swam them closer to the shallows.

"S-she's coming here," Eddie whispered with a squeak of fear.

The fish-tailed creature shoved Ben onto the rocks, keeping her long tail – with its shimmering blue, green, and gold scales, partially in the water. Long waves of her dripping hair trailed down her nearly-flat chest as she glanced over their group with stunning green eyes.

"Is Ben okay?" Eddie asked, taking a hesitant step forward.

In a flash, the mermaid bared surprisingly sharp teeth at them, her eyes narrowed into slits as she hissed loudly. They could see her sharp claw-like nails digging into the rocky ground as she crouched over Ben's unconscious body. Then, something strange happened, the mermaid seemed to have a change of heart. She made a sighing sound, her posture becoming less threatening as she turned her gaze back on the chubby boy beneath her. Seconds later, the beautiful creature was pressing her lips to Ben's.

"Whoa," Richie whispered, adjusting his glasses.

Eddie twitched as he watched, wondering if he should try to take over. It seemed like she was trying to do the Heimlich maneuver, but…

 **SLAP!**

The boys all jumped at the frustrated growl that left the mermaid's lips, before those lips were pressed against Ben's again.

A jolt of relief went through the group when their newest friend breathed in, his entire body surging like he'd been struck by lightning. The mermaid seemed distracted as Ben began to hack and cough up the water from his lungs.

"W-what's going on? Eeep!" Ben's eyes were riveted to the creature perched above him.

"The mermaid totally _smooched_ you back to life!" Richie yelled, making Eddie and Stanley wince at the volume of his voice.

"Mer-maid?" the creature hissed angrily, its brilliant tail splashing the water in annoyance. The deeper note to its voice suggested that it, perhaps, was not a female as they first suspected.

"Sorry, um, merboy?" Stanley suggested uncertainly.

"S-s-siren. And I am clearly _NOT_ female," the creature hissed, his green eyes riveted on Richie.

"I've read about you," Eddie commented, catching the siren's attention. He didn't like the way the young man – creature – thing was staring at his friend. "You… you sing sailors into the ocean, and watch them drown."

"Some of us do," the creature agreed, shrugging his shoulders as if it was absolutely normal to murder people. Those green eyes turned back to Ben, and the siren asked, "Why were you throwing stale fish into the water, human child?"

Ben fumbled for an answer. "Um… We wanted to feed you. T-there's not many fish in this river now that it's closed off by the dam."

"Dam?"

"It's like a big wall that keeps the water from getting too high," Stanley explained.

The siren's eyes narrowed into slits as he hissed under his breath. In an attempt to appease the creature, before he did something like sing them all to their deaths, Eddie rushed to apologize. "We're sorry. We didn't make the dam, the adults did."

"I do not blame you," the siren growled, pushing himself back into the water until he was chest deep. Green eyes stayed on them for a long moment, before the siren spoke again. This time - with a _warning_.

"It is not safe for children to venture here so late in the day. A predator lives nearby."

"Did you like the fish?" Richie suddenly asked.

"I prefer freshly-killed meat," the siren answered haughtily, giving them another glimpse of razor-sharp teeth as his lips curled upward – likely in delight at the thought of a meal.

"You – you don't eat people, do you?" Eddie asked, unconsciously clutching Richie's arm for comfort.

"I do not eat human children," the siren answered mysteriously.

"Do you eat adults?" Stanley questioned, frowning at the creature.

The siren shrugged. "Meat is meat… Now, you really must leave. I cannot protect you after dark."

"Will you be here tomorrow?" Ben asked, pushing himself to his feet.

"Where else would I be?" the creature answered, before he slipped back under the water. The boys were given one last glimpse of his brilliant tail, before the siren disappeared.

* * *

Note: I'll admit, I'm taking a bit of liberty with the location. I like the idea of siren Billy swimming beneath the waterfall, but also having access to Pennywise's main sewer line. Not exactly sure if that's the way it is on the official Derry map, but that's where I've set the location in the story.


	3. The Mating Habits of Sirens

**Ch 3: The Mating Habits of Sirens**

* * *

The creature known as Pennywise had been on Billy's mind for the last several nights. Ever since Billy met IT, the clown had been overly eager to bring him fresh meat, and had even extended an open invitation to co-exist in its territory. The red-haired creature had seemed more than delighted to hear Billy's song, even if the lure did not have the same hold on it as it did on humans.

In fact, Billy realized with a jolt of insight, if Pennywise had been a siren, his _courting_ would have been obvious long before now. The thought of an attentive mate – even if it was a strange land-dweller, was enough to cause the siren to churn the water with his tail in delight. Perhaps he could convince Pennywise to swim with him sometime soon.

* * *

The other monster was eyeing HIS boys, Billy realized, watching as the children tromped off through the woods on their way home. Pennywise was not being subtle about it. The siren huffed aloud, and swam closer to shore, keeping his gaze on his future mate. A human would have called him obsessed with the idea of having the clown as a mate, but Billy didn't care. He'd already decided to keep IT.

"Penny, come closer to the water," the siren sang out, once he was sure the boys were out of earshot. The pale-skinned creature turned to look at him, its bloodlust sated by the siren's interest.

The clown made his way to the water's edge, and Billy purred as he drew himself up onto the bank, letting his brilliantly-scaled tail (if he did say so himself) drift leisurely in the water.

"You've been spending time with those boys," Pennywise observed.

"I have. It gets boring in this closed-off river, and they amuse me with their questions. And the cute noises they make when I kiss them," Billy sighed, leaning back to, not so subtly, show off his stomach. A sign of submission, such as this, would not go unnoticed by another predator – and Billy liked the way the other creature's shimmering blue eyes lingered on his flesh.

"Do you often… k-kiss them?" Pennywise asked. Billy noted, with amusement, that the clown's white gloves were beginning to split open with the emergence of his black claws.

"Mmm… Sometimes. I do like kissing," the siren purred, rolling onto his stomach and propping up his chin to watch his future mate growl under its breath.

"And if I killed one of them… what would you do?" Pennywise suddenly asked, its blue eyes turning such a brilliant gold that it sent a shiver of arousal down Billy's back.

"Don't kill them," the siren whispered, his heart quickening under the other creature's gaze. Licking his lips, Billy pushed himself back into the water, making sure to keep the clown in his sights. It wouldn't do for his mate to sneak off, after all. Not when the full moon would soon be shining so perfectly above them.

Pennywise's eyes returned to their blue hue as it watched the siren float only a short distance away.

"Swim with me," Billy sang out, flicking his tail to send a teasing splash of water at the clown. "I've seen you change shapes. Surely you can make yourself a tail, and join me in the water."

The clown, for once, seemed utterly bewildered by the request. "What is so interesting about the water?" Pennywise finally asked, tilting its head to observe him.

"It is not the _water_ that is interesting," Billy purred, licking his lips as he thought about having HIS, soon to be, mate all to himself.

"Very well," Pennywise agreed.

Billy blinked, and the clown was gone. There was not even a splash to suggest it had gotten into the water. Glancing around, the siren realized that the other creature had left him all alone, with no intention of joining him.

 **HOW DARE IT TOY WITH HIS FEELINGS!**

The siren lashed his tail furiously, before diving down into the depths to scream his fury to the corpses hidden around HIS home. A familiar pair of blue eyes were suddenly ahead of him, and Billy drew back with a startled hiss. Blinking his eyes rapidly, the siren found himself staring at beautiful young man with a long golden tail.

"Looking for me," the other siren asked, clearly delighted to have frightened him.

Billy didn't answer right away. Instead, he took the time to swim around the other siren, noting his dark hair and deliciously-chiseled chest.

"Didn't you promise to show me what was so interesting about this river? After all, I did go through the trouble of making this new form – Just For You," Pennywise insisted.

Billy felt his heart race at the thought. Pennywise really would be the perfect mate. And he was not ashamed to tell him just that.

The former-clown's smirk fell from its face, replaced by the same bewilderment as before. As if it couldn't imagine why Billy would make such a strange request of it.

"You will be my mate, won't you? You welcomed me into your territory, and kept me well fed. You like my singing, and…" Billy swam closer, wrapping his tail around the new siren's own. "And the thought of you excites me. I want you to be my one. Sirens mate for life, you know."

"Can I still eat your boys?" Pennywise suddenly asked. The abruptness of its question made Billy laugh.

"No, you may not. But if you're here to give me kisses, I won't need to get them from my boys – will I?" The former-clown seemed to like the idea, as its strong arms wrapped around Billy's waist, and he was drawn into that _**perfect first kiss.**_

* * *

Note: And that's all she wrote. Glad you enjoyed reading. I'm still working on Monster Club, and several short IT ficlets, as well.


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